Mixer assembly for mixing an additive with an exhaust gas flow

ABSTRACT

A mixer arrangement for mixing an additive with an exhaust-gas flow, having an exhaust-gas line, an exhaust gas flowing through the exhaust-gas line in a main flow direction, and having at least one exhaust-gas purification element which is arranged in the exhaust-gas line and which has a casing and, arranged within the casing, a flow-over surface for the exhaust gas. Here, the casing of the at least one exhaust-gas purification element has a guide structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of PCT ApplicationPCT/EP2016/076308, filed Nov. 1, 2016, which claims priority to GermanPatent Application 10 2015 221 438.9, filed Nov. 2, 2015, and GermanPatent Application 10 2015 221 432.2, filed Nov. 1, 2015. Thedisclosures of the above applications are incorporated herein byreference.

FIELD OF THE INVENTION

The invention relates to a mixer arrangement for mixing an additive withan exhaust-gas flow, having an exhaust-gas line, an exhaust gas flowingthrough the exhaust-gas line in a main flow direction, and having atleast one exhaust-gas purification element which is arranged in theexhaust-gas line and which has a casing and, arranged within the casing,a flow-over surface for the exhaust gas.

BACKGROUND OF THE INVENTION

In internal combustion engines, in particular diesel engines orlean-burn engines, undesirably high quantities of nitrogen oxides areformed. A suitable approach for the elimination of these is inparticular the addition of the additive ammonia, whereby, in thepresence of an excess of oxygen, the nitrogen oxides can be reduced toform nitrogen, and the hydrogen fraction of the ammonia bonds to formwater.

It is known for additive to be introduced into the exhaust-gas line.With the exhaust-gas flow, the additive is transported to a selectivereduction catalytic converter (SCR catalytic converter). With theinjection of the additive counter to the main flow direction of theexhaust-gas flow, it is sought to achieve uniform mixing of the additivewith the exhaust gas. From DE 10 2011 117 139 A1, it is known to providea depression in the exhaust-gas line. By means of the depression, it issought to realize swirling of the exhaust gas in the exhaust-gas line inorder to further improve the mixing with the additive. It has howeverbeen found that even such depressions, despite the swirling that isgenerated, generate an uneven droplet load of the additive in relationto the cross-sectional area of the exhaust-gas line. To achieve highnitrogen oxide reduction rates, a highly uniform concentrationdistribution of the additive and a uniform temperature distribution, inparticular with regard to the relatively cold edge region, are necessaryover the cross section of the exhaust-gas line upstream of the SCRcatalytic converter. A further disadvantage consists in that suchdepressions are associated with an enlargement of the cross section ofthe exhaust-gas line, whereby the exhaust-gas line requires a largerstructural space.

SUMMARY OF THE INVENTION

The invention is therefore based on the object of providing an apparatuswith which high nitrogen oxide reduction rates are achieved.

The object is achieved according to the invention in that the casing ofthe at least one exhaust-gas purification element has a guide structure.

The guide structure is in this case not a functional element of theexhaust-gas purification element, in particular of the flow-over surfacearranged within the casing. The guide structure is arranged as anadditional functional unit on the at least one exhaust-gas purificationelement. With the arrangement of the guide structure on the casing, itis possible for influencing of the exhaust-gas flow and thus swirling ofthe exhaust-gas flow to be achieved in a particularly simple andeffective manner. The swirling is significantly conducive to achievingthat the additive supplied in droplet form to the exhaust-gas flow isdistributed more uniformly over the entire cross section of theexhaust-gas line, and thus the exhaust-gas aftertreatment takes place ina manner distributed more uniformly over the entire cross section.Likewise, as a result of the mixing, the temperature in the end regionis increased, whereby a more uniform temperature distribution isrealized. Owing to the improved utilization of the cross section, theaftertreatment rate of the exhaust gas increases, or the length of theexhaust-gas treatment path is shortened while achieving the sameaftertreatment rate. The arrangement on the casing furthermore has theadvantage that, in this way, an inexpensive fastening of the guidestructure to an exhaust-gas purification element is realized. Anadditional carrier structure for the fastening of the guide structure istherefore not necessary. Furthermore, by means of the design of theguide structure, an adaptation of the swirling to the respectiveexhaust-gas line is achieved.

The adaptation of the swirling of the exhaust-gas flow by means of thedesign of the guide structure is achieved in a particularly simplemanner by virtue of the guide structure having multiple guide elements.

In a further advantageous embodiment, the guide structure is generatedin a particularly simple manner by virtue of the guide structure beingformed in one piece with the casing. In particular in the case of acasing produced from sheet metal, the guide structure is generated bymeans of corresponding cutting-out of the sheet-metal casing in the sameworking step. The fastening of the guide structure to the casing isthereby eliminated.

In a further advantageous embodiment, the guide structure is connectedto the casing. This refinement has the advantage that the handling ofthe casing and guide structure during the production and assemblyprocesses is easier. The fastening of the guide structure to the casingmay advantageously be realized by means of welding or stapling, forexample by induction welding. It is likewise conceivable for the guidestructure to be fastened to the casing by means of rivets or screwconnections. A further advantage consists in that, by means of thesolution according to the invention, existing exhaust-gas purificationelements are enhanced to include the guide structure.

A fastening of the guide structure to the casing of the exhaust-gaspurification element without additional fastening means is achieved ifthe guide structure is pressed together with the casing. Here, the guidestructure may either be pressed into the casing or pressed onto thecasing. The pressing of the guide structure into the casing has theadvantage that the guide structure does not increase the outer diameterof the exhaust-gas purification apparatus, such that no additionalstructural space is required with regard to the outer diameter.

In a particularly simple embodiment, the guide structure is acylindrical component, the casing surface of which has at least oneradially inward indentation. It is preferable for 2 to 10, particularlypreferably 3 to 8, indentations to be provided. Since the indentationsare intended to generate swirling, the demands on the dimensionalaccuracy of the indentations are low, whereby the guide structureaccording to the invention is manufactured at relatively low cost.

A particularly good adaptation of the swirling of the exhaust-gas flowto the respective exhaust-gas line is achieved, in a furtheradvantageous embodiment, in that the guide structure has at least twoguide elements, preferably 3 to 20 guide elements, in particular 4 to 10guide elements.

The swirling in the exhaust-gas flow is improved if the guide elementsare at least partially bent radially inward in the direction of the axisof symmetry of the exhaust-gas line. Here, “at least partially bent” isto be understood to mean that the entire guide element or only a part ofthe guide element is bent inward. Here, in the context of the invention,a bend refers both to a discontinuous profile of the guide element, suchas arises in the case of a kink, and a continuous profile of the guideelement, if the bend is described with a radius.

Improved swirling may also be achieved by virtue of the guide elementbeing multiply bent. Here, it is conceivable that, in the flowdirection, the guide element may be initially bent initially inward andsubsequently also bent outward again in the direction of the wall of theexhaust-gas line.

Further setting of the swirling of the exhaust-gas flow is easilyachieved by virtue of the individual guide elements having differentsizes and/or bends. In this way, swirling patterns in the exhaust-gasflow that repeat in relation to the circumferential direction isminimized. These would otherwise result in swirling being generated overa particular sector, but swirling over the entire circumference of theexhaust-gas flow being impeded.

In order that the guide elements project as far as possible into theexhaust-gas flow, they must have a certain length. If the guide elementsare oriented parallel to the casing axis in the case of an unwoundcasing, the required length of the metal sheet for the productionthereof is defined by the axial length of the casing and the length ofthe guide elements. In a further advantageous embodiment, the length ofthe metal casing sheet required for production purposes are considerablyreduced if the guide elements are oriented at an angle with respect tothe casing. By means of this orientation, the guide elements have aconsiderably smaller axial extent. In this way, the production costs arereduced.

In a simple embodiment, all of the guide elements are formed with thesame shape. This has the advantage that a punching tool for theproduction of the guide elements may be designed to be inexpensive.

Improved swirling of the gas flow is achieved with asymmetricallydesigned guide elements. Asymmetrical means that the guide elements havefor example an area which deviates from a rectangular shape.

In another embodiment, it is likewise possible for in each case twoadjacent guide elements to have different areas through variation of therespective lengths and widths.

By means of these different shapes of the guide elements, it is soughtto prevent partially identical swirling patterns from arising, whichcollectively permit little swirling over the entire cross section of theexhaust-gas flow.

In a further advantageous embodiment, to further intensify the swirling,the guide elements have substructures. Such substructures may beembossments, perforations or incisions in the end regions, wherein, inthe case of the incisions in the end regions, the individual regions maybe additionally bent.

Different arrangements of the guide structure may be advantageousdepending on the field of use, that is to say specifically thegeometrical form of the exhaust-gas line, the exhaust-gas flow withregard to throughflow rate and temperature, the exhaust-gas purificationelements used and the arrangement thereof.

The flow-over surfaces used in exhaust-gas purification elementsgenerally give rise to a certain laminarization of the exhaust-gas flowwithin the exhaust-gas purification element and when the exhaust gasexits the exhaust-gas purification element. The laminar flows not onlyhave the disadvantage that they give rise to and maintainnon-uniformities that arise during the injection of the additive. Theyalso have the effect that they maintain the temperature gradients thatarise in the exhaust-gas flow. Such temperature gradients arise as aresult of exhaust-gas purification elements having a relatively lowtemperature radially at the outside. The exhaust-gas aftertreatment istherefore less intensive in the regions. In one advantageous embodiment,the formation of such temperature gradients in the adjoining section ofthe exhaust-gas line is avoided by virtue of the guide structureaccording to the invention being arranged on the downstream-facing sideof the casing of the exhaust-gas purification element. The swirling thusgenerated of the emerging flow counteracts the formation of suchtemperature gradients in the adjoining section of the exhaust-gas line.The exhaust gas mixes over the entire cross section of the exhaust-gasline, and the exhaust-gas aftertreatment is thus improved.

This embodiment is furthermore also advantageous if the exhaust-gasaftertreatment is performed using multiple exhaust-gas purificationelements and the guide structure is arranged on at least one of thoseexhaust-gas purification elements which is positioned upstream of thefinal exhaust-gas purification element as viewed in the flow direction.

In another advantageous embodiment, the guide structure is arranged onthe casing on the upstream-facing side of the exhaust-gas purificationelement. This is advantageous in particular if the exhaust-gas flow fedto the exhaust-gas purification element is laminar and thus hastemperature gradients in relation to the cross section of theexhaust-gas line. For these situations, the laminar flow is changed intoa turbulent flow by means of the guide structure arranged upstream. Inthis way, the exhaust-gas purification element is impinged on by a flowwithout temperature gradients, which results in an improved temperaturedistribution in the exhaust-gas purification element and thus improvedexhaust-gas aftertreatment. This is advantageous in particular in thecase of catalytic converters in which the temperature distribution has aparticularly great influence on the effectiveness, such as for examplecatalytic converters for methane oxidation. Likewise, with the changefrom a laminar to a turbulent flow, the droplet distribution of asupplied additive in relation to the cross section is more uniform.

The arrangement according to the invention of a guide structure isfurthermore not restricted to particular structural forms of exhaust-gaspurification elements. Aside from exhaust-gas purification elements withcylindrical honeycomb bodies, the guide structure may also be providedin the case of so-called ring-shaped catalytic converters. Ring-shapedcatalytic converters are exhaust-gas purification elements which have acylindrical recess in their center, in the manner of a hollow cylinder,and the honeycomb body extends around the cylindrical recess. Theexhaust-gas purification element requires no additional structural spacein an axial direction if the guide structure does not extend beyond theaxial extent of the honeycomb body. Furthermore, the guide structurewith the above-described embodiments are applied to hollow cylindricalhoneycomb bodies.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be discussed in more detail on the basis of multipleexemplary embodiments. In the figures:

FIG. 1 is a schematic illustration of a mixer arrangement;

FIG. 2-4 show further arrangements of a mixer arrangement as per FIG. 1,

FIG. 5 shows an exhaust-gas purification element with a flow-oversurface,

FIG. 6 shows the casing of an exhaust-gas purification element,

FIG. 7-9 show guide elements of the guide structure,

FIG. 10 shows a further embodiment of a mixer arrangement.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

FIG. 1 shows a mixer arrangement having an exhaust-gas line 1 in a motorvehicle (not illustrated in any more detail). The arrow indicates themain flow direction of the exhaust gas flowing through the exhaust-gasline 1. By means of an injector 2 arranged on the exhaust-gas line 1,urea solution is injected into the exhaust-gas flow at an angle withrespect to the main flow direction, such that the jet 3 strikes anexhaust-gas purification element 4 approximately centrally. Theexhaust-gas purification element is an SCR catalytic converter 4. TheSCR catalytic converter 4 is composed of a schematically illustratedhoneycomb body 5, which forms a flow-over surface for the exhaust gas,and a casing 6, which fully encloses the honeycomb body 5. On thedownstream-facing side 7 of the casing 6, a guide structure 8 isfastened to the casing 6. The construction of the guide structure 8 isdescribed in the following figures. During the operation of the mixerarrangement, the injected urea solution is sprayed onto the honeycombbody 5 and is transported through the honeycomb body 5 by the exhaustgas. Owing to the structure of the flow-over surface, the exhaust gasand the droplets of urea solution still contained therein emerge fromthe honeycomb body 5 on the side 7 substantially as a laminar flow. Theguide structure 8 disrupts the laminar flow, such that, downstream ofthe guide structure 8 in the flow direction, the laminar flow is causedto swirl and thus changes into a turbulent flow. As a result of thisswirling, more exhaust gas comes into contact with the droplets of theurea solution, whereby the efficiency of the exhaust-gas after treatmentis increased.

The mixer arrangement in FIG. 2 is composed of the exhaust-gas line 1and two SCR catalytic converters 4, 4′ as exhaust-gas purificationelements. Both SCR catalytic converters 4, 4′ have in each case onehoneycomb body 5 and one casing 6 surrounding the honeycomb body. TheSCR catalytic converter 4 arranged upstream of the final SCR catalyticconverter 4′ as viewed in the flow direction has a guide structure 8 onits downstream-facing side 7. By means of the guide structure 8, theflow emerging from the SCR catalytic converter 4 is caused to swirl,such that a thoroughly mixed exhaust-gas flow enters the downstream SCRcatalytic converter 4′. As a result of this swirling, hot exhaust gasfrom the center of the SCR catalytic converter 4 is mixed with the lesshot exhaust gas from the regions in the vicinity of the casing 6, suchthat exhaust gas entering the SCR catalytic converter 4′ exhibitsgreater temperature homogeneity in relation to the cross section, whichincreases the efficiency of the second SCR catalytic converter 4′.

The mixer arrangement as per FIG. 3 may be regarded as a combination ofthe mixing arrangements from FIGS. 1 and 2. The guide structure 8 causesswirling of the exhaust-gas flow emerging from the SCR catalyticconverter 4, whereby the exhaust-gas flow entering the SCR catalyticconverter 4′ exhibits a more uniform distribution both with regard tothe temperature distribution but also with regard to the dropletdistribution of the injected urea solution. In particular in the case ofthe distribution of the urea solution, the guide structure 8 assists thejet 3 in order to distribute the urea solution more uniformly over theentire cross section.

The mixer arrangement shown in FIG. 4 differs with regard to theexhaust-gas purification element 4. The latter has a guide structure 8on the upstream-facing side 9 of the casing 6. Thus, the impingingexhaust-gas flow is influenced with a swirling action by the exhaust-gaspurification element 4 to which the exhaust-gas flow is supplied.

FIG. 5 shows a plan view of an exhaust-gas purification element 4, inparticular an SCR catalytic converter. The exhaust-gas purificationelement is composed of a casing 6 in which a honeycomb body 5 isarranged. The honeycomb body 5 is composed of a multiplicity ofinterconnected foil layers, which form the flow-over surface for theexhaust gas. The casing 6 has a greater length than the honeycomb body5. The guide structure 8 is fastened to the inner side of the freecasing surface by means of induction welding. The guide structure 8 iscomposed of an encircling ring 10 which bears against the inner side ofthe casing 6. Guide elements 11 extend in an axial direction from thering 10. The guide elements 11 all have the same area and shape and arebent radially inward by virtue of the guide elements 11 being kinked indiscontinuous fashion along an edge, such that they project at an angleof between 0° and 90° into the exhaust-gas flow.

In FIG. 6, the guide structure 8 with the guide elements 11 is formed inone piece with the casing 6 of the SCR catalytic converter 4. The casingtube 6 is illustrated in unwound form. For the production of the casing6, the casing tube is rolled up, such that the two outer edges 13, 14abut against one another. The casing 6 may subsequently be welded. Alongthe edges 12, the guide elements 11 are bent at the desired angle. Tointensify the mixing and to avoid partial swirling patterns, adjacentguide elements 11 have different shapes. This is achieved throughvariation of the lengths and widths of the guide elements 11 but also bymeans of bends at different angles.

The following figures show different guide elements 11. The guideelement in FIG. 7 has a multiplicity of apertures 15, such that, as aresult of the passage from one side of the guide element 11 to the otherside, the exhaust gas intensifies the thorough mixing of the exhaust-gasflow. Thorough mixing is also realized even if, in this arrangement,depressions 15 are arranged in place of the apertures, which depressionsproject as protuberances on the opposite side of the guide element 11.These substructures effect additional swirling and thus improve thethorough mixing.

FIG. 8 shows a guide element 11 that has not yet been bent in a sideview, which guide element has incisions on the circumference as asubstructure, and individual regions 16 are bent in the manner oftongues out of the plane of the guide element 11.

The guide element 11 in FIG. 9 has a first region 17, in which the guideelement 11 has been bent radially inward. In a second region 18, theguide element has been bent in the opposite direction thereto. By meansof both regions 17, 18, the guide element 11 has a twist about itslongitudinal axis 19.

FIG. 10 shows a further embodiment of a mixer arrangement, which isdirected substantially to the embodiment of the honeycomb body 5 of theexhaust-gas purification element 4. The honeycomb body 5 is formed as ahollow cylinder with a cylindrical recess 20 situated in the center. Theguide structure 8 is arranged in the cylindrical recess 20, preferablyon the wall, which delimits the honeycomb body 5 in a radially inwarddirection, of the casing 6. In the illustration shown, the guidestructure 8 is arranged at the downstream-facing end of the exhaust-gaspurification element 4. It is however also conceivable for the exemplaryembodiments described in the above figures to be applied to a honeycombbody 5 as per FIG. 10.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

What is claimed is:
 1. A mixer arrangement for mixing an additive withan exhaust-gas flow, comprising: an exhaust-gas line; at least oneexhaust-gas purification element which is arranged in the exhaust-gasline; a casing; a flow-over surface for the exhaust gas, the flow-oversurface arranged within the casing; a guide structure connected to thecasing of the at least one exhaust-gas purification element; wherein anexhaust gas flows through the exhaust-gas line in a main flow direction.2. The mixer arrangement of claim 1, the guide structure furthercomprising multiple guide elements.
 3. The mixer apparatus of claim 2,wherein the multiple guide elements are at least partially bent radiallyinward.
 4. The mixer apparatus of claim 2, further comprising an unwoundcasing, wherein the multiple guide elements are, in the unwound casing,arranged at an angle with respect to the axial extent of the casing. 5.The mixer apparatus of claim 2, wherein each of the multiple guideelements further comprising the same shape.
 6. The mixer apparatus ofclaim 2, wherein the multiple guide elements are of asymmetrical design.7. The mixer apparatus of claim 2, wherein two adjacent multiple guideelements have different areas.
 8. The mixer apparatus of claim 2, themultiple guide elements further comprising substructures.
 9. The mixerapparatus of claim 8, the substructures in the guide elements furthercomprising embossments.
 10. The mixer apparatus of claim 8, thesubstructures in the guide elements further comprising perforations. 11.The mixer apparatus of claim 8, the substructures further comprisingincisions in the end regions of the respective guide element.
 12. Themixer apparatus of claim 11, wherein, in the case of the incisions inthe end regions, the individual regions may be additionally bent. 13.The mixer arrangement of claim 1, wherein the guide structure is formedin one piece with the casing.
 14. The mixer arrangement of claim 1,wherein the guide structure is connected to the casing.
 15. The mixerarrangement of claim 1, wherein the guide structure is connected to thecasing using inductive welding.
 16. The mixer apparatus of claim 1,wherein the guide structure is arranged on the downstream-facing side ofthe casing of the exhaust-gas purification element.
 17. The mixerapparatus of claim 1, wherein the guide structure is arranged on theupstream-facing side of the casing of the exhaust-gas purificationelement.
 18. The mixer apparatus of claim 1, the at least oneexhaust-gas purification element further comprising multiple exhaust-gaspurification elements, wherein the multiple exhaust-gas purificationelements are arranged in the exhaust-gas line.
 19. The mixer apparatusof claim 18, wherein the guide structure is arranged on at least one ofthe multiple exhaust-gas purification elements which is positionedupstream of another of the multiple exhaust-gas purification elements asviewed in the flow direction.
 20. The mixer arrangement of claim 1, thehoneycomb body further comprising a hollow cylinder with a radiallyinternally situated cylindrical recess.